This invention is in the field of control cards for gaining access. More particularly it is for gaining access to a restricted area, or access to restricted material or papers, or access to money, tickets, checks and the like.
In the prior art there have been many types of control cards described. All of these attempt, in one way or another, to provide some crucial test, which can be performed on the card so as to determine whether it is authentic, or a copy or forgery. All of the physical properties of the prior art cards were capable of being copied, and therefore the tests of validity or authentication were of little value.